package com.gitee.wsl.mathematics.function.noise

import kotlin.math.floor


/**
 * Represents a simple Perlon noise generator
 * This generates smooth noise which gives a normal distribution of random values.
 * Perlin noise https://en.wikipedia.org/wiki/Perlin_noise
 * from: https://rosettacode.org/wiki/Perlin_noise#Kotlin
 */
object Perlin {
    private val permutation = intArrayOf(
        151, 160, 137, 91, 90, 15, 131, 13, 201, 95, 96, 53, 194, 233, 7, 225,
        140, 36, 103, 30, 69, 142, 8, 99, 37, 240, 21, 10, 23, 190, 6, 148,
        247, 120, 234, 75, 0, 26, 197, 62, 94, 252, 219, 203, 117, 35, 11, 32,
        57, 177, 33, 88, 237, 149, 56, 87, 174, 20, 125, 136, 171, 168, 68, 175,
        74, 165, 71, 134, 139, 48, 27, 166, 77, 146, 158, 231, 83, 111, 229, 122,
        60, 211, 133, 230, 220, 105, 92, 41, 55, 46, 245, 40, 244, 102, 143, 54,
        65, 25, 63, 161, 1, 216, 80, 73, 209, 76, 132, 187, 208, 89, 18, 169,
        200, 196, 135, 130, 116, 188, 159, 86, 164, 100, 109, 198, 173, 186, 3, 64,
        52, 217, 226, 250, 124, 123, 5, 202, 38, 147, 118, 126, 255, 82, 85, 212,
        207, 206, 59, 227, 47, 16, 58, 17, 182, 189, 28, 42, 223, 183, 170, 213,
        119, 248, 152, 2, 44, 154, 163, 70, 221, 153, 101, 155, 167, 43, 172, 9,
        129, 22, 39, 253, 19, 98, 108, 110, 79, 113, 224, 232, 178, 185, 112, 104,
        218, 246, 97, 228, 251, 34, 242, 193, 238, 210, 144, 12, 191, 179, 162, 241,
        81, 51, 145, 235, 249, 14, 239, 107, 49, 192, 214, 31, 181, 199, 106, 157,
        184, 84, 204, 176, 115, 121, 50, 45, 127, 4, 150, 254, 138, 236, 205, 93,
        222, 114, 67, 29, 24, 72, 243, 141, 128, 195, 78, 66, 215, 61, 156, 180
    )

    private val p = IntArray(512) {
        if (it < 256) permutation[it] else permutation[it - 256]
    }

    fun noise(x: Double, y: Double, z: Double): Double {
        // Find unit cube that contains point
        val xi = floor(x).toInt() and 255
        val yi = floor(y).toInt() and 255
        val zi = floor(z).toInt() and 255

        // Find relative x, y, z of point in cube
        val xx = x - floor(x)
        val yy = y - floor(y)
        val zz = z - floor(z)

        // Compute fade curves for each of xx, yy, zz
        val u = fade(xx)
        val v = fade(yy)
        val w = fade(zz)

        // Hash co-ordinates of the 8 cube corners
        // and add blended results from 8 corners of cube

        val a = p[xi] + yi
        val aa = p[a] + zi
        val ab = p[a + 1] + zi
        val b = p[xi + 1] + yi
        val ba = p[b] + zi
        val bb = p[b + 1] + zi

        return lerp(
            w,
            lerp(
                v,
                lerp(
                    u, grad(p[aa], xx, yy, zz),
                    grad(p[ba], xx - 1, yy, zz)
                ),
                lerp(
                    u, grad(p[ab], xx, yy - 1, zz),
                    grad(p[bb], xx - 1, yy - 1, zz)
                )
            ),
            lerp(
                v,
                lerp(
                    u, grad(p[aa + 1], xx, yy, zz - 1),
                    grad(p[ba + 1], xx - 1, yy, zz - 1)
                ),
                lerp(
                    u, grad(p[ab + 1], xx, yy - 1, zz - 1),
                    grad(p[bb + 1], xx - 1, yy - 1, zz - 1)
                )
            )
        )
    }

    private fun fade(t: Double) = t * t * t * (t * (t * 6 - 15) + 10)

    private fun lerp(t: Double, a: Double, b: Double) = a + t * (b - a)

    private fun grad(hash: Int, x: Double, y: Double, z: Double): Double {
        // Convert low 4 bits of hash code into 12 gradient directions
        val h = hash and 15
        val u = if (h < 8) x else y
        val v = if (h < 4) y else if (h == 12 || h == 14) x else z
        return (if ((h and 1) == 0) u else -u) +
                (if ((h and 2) == 0) v else -v)
    }
}